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Old 14th Oct 2019, 9:31 am   #107
ms660
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Join Date: Apr 2011
Location: Cornwall, UK.
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Default Re: Philips BX281U20 valve radio

Quote:
Originally Posted by Croozer View Post
To bring the 220V set to a condition for operation on your mains (245v?) It will be necessary to add a resistor. This should come after the on off switch and be in series with the existing dropper.

(It should not be in shunt (parallel) across the on off switch)

To calculate the resistance required we need to know the volts to be dropped as discussed before (20 -25V ). We also need to know the total current consumption of the set ie. The heaters plus the HT.

We know the heater current is 100mA

For the HT current, we can either (i) measure it using ohms law. We know all and only the HT current flows through R1, so by measuring the resistance of R1 and the voltage drop across it,we can calculate the current from I =V/R
All the HT current doesn't flow through R1....

Then there's the ripple current....

Lawrence.
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